Interesting stuff. I basically skimmed through it (there's a lot of material there) but it's a pretty detailed series of articles on how a piston head went about designing a recumbent trike from automotive engineering principles. The discussion on chassis and suspension geometry is particularly good, lots of info on how to go about designing a suspension system that will perform well. It also highlights how much more complicated these things get when you've got three or more wheels... bike geometry is so much simpler.